Journal of Biology and Nature

Background: Environmental pollutants such as cadmium (Cd) pose a significant threat to neuronal health by inducing oxidative stress, neuronal damage, and behavioural impairments, particularly within the hippocampus, a critical brain region for learning, memory, and social behaviours. Amaranthus hybridus, a leafy vegetable rich in flavonoids and phenolic compounds, has shown promise as a natural antioxidant with potential neuroprotective effects. However, its efficacy against cadmium-induced hippocampal neurotoxicity and associated behavioural deficits remains underexplored.

Aim: This study aimed to evaluate the protective effects of A. hybridus leaf ethanol extract (EEAH) and flavonoid-rich extract (FREAH) against cadmium-induced hippocampal CA2 neurotoxicity and social behavioural impairments in Wistar rats.

Methods: Thirty-six adult male Wistar rats weighing 70–140 g were randomly assigned to six groups of six animals each: control, cadmium-only (5 mg/kg), cadmium + EEAH (500 mg/kg), cadmium + FREAH (500 mg/kg), EEAH alone, and FREAH alone. Cadmium and the extracts were administered concurrently by oral gavage for 8 weeks. Behavioural assessments included social recognition tests measuring investigation time, discrimination index, habituation rate, and novel preference. After administration, hippocampal tissues were subjected to histological analysis (H&E staining), and biochemical assays measured the oxidative stress markers superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and malondialdehyde (MDA). Data were analysed using one-way ANOVA, with p < 0.05 considered statistically significant.

Results: Cadmium exposure significantly impaired social recognition behaviour, reducing investigation times in the familiar (10.24 seconds) (p < 0.05) and novel phases (16.73 seconds) (p < 0.05), with a decreased discrimination index (24.01%) (p < 0.05) and habituation rate (38.22%) (p < 0.05). Histologically, cadmium caused disorganisation of hippocampal CA2 neurons, with vacuolations and gliosis; these changes were notably ameliorated by A. hybridus extracts, especially FREAH, with familiar (16.91 seconds) (p < 0.05) and novel phases (30.53 seconds) (p < 0.05), a discrimination index of 28.72% (p < 0.05), and a habituation rate of 52.43% (p < 0.05). Biochemically, cadmium elevated MDA (10.77 µmol/ml/mg) (p < 0.05) and decreased SOD (37.13 µmol/ml/mg), CAT (32.54 µmol/ml/mg), and GSH (19.63 µmol/ml/mg) activities (p < 0.05), indicating oxidative stress. Both EEAH and FREAH significantly reduced MDA (6.47 µmol/ml/mg) (p < 0.05) and normalised antioxidant enzyme levels closer to control values, with FREAH SOD (59.23 µmol/ml/mg), CAT (57.38 µmol/ml/mg), and GSH (26.22 µmol/ml/mg) activities (p < 0.05) demonstrating superior efficacy.

Conclusion: Amaranthus hybridus leaf extracts, particularly the flavonoid-rich extract, exhibited significant neuroprotective effects against cadmium-induced hippocampal neurotoxicity and behavioural deficits. These findings suggest that A. hybridus could serve as a natural therapeutic agent for mitigating the adverse effects of environmental neurotoxins and improving neurobehavioural outcomes.